Erythromycin and Cipro are both on the QT drug list that can cause prolongation of the QT interval on an ECG and can cause the arrhythmia Torsades de pointe. This is usually worse for patients with Long QT Syndrome or for people taking anti arrhythmic drugs or other drugs also on the QT Drug list. Check it out at www.****.org.
The 4 listed on the site were Hismanal, Propulsid, Orap and Seldane. Hope that helps.
I googled the med and there are plenty of sites for information. From what I see erythro is not in the same class of drugs as penicillin. As for heart arrhythmias, it seems to be dangerous only if you're taking certain other drugs at the same time. I don't recognize the meds that were listed so it would be better for you to check it for yourself. See if any of those ring a bell for you.
I have taken erythromycin in years past, usually for respiratory problems. All I had was nausea from the med which is common. It didn't affect my heart at all. I've also taken Cipro for campylobacter, an intestinal bug, no problem with that either.
If your doctor knows you're sensitive to penicillin, they can choose a different medication. You can double check with the pharmacist when you go in to pick it up as well. They know the drugs the best; that's their job.